The present invention relates to a document reading apparatus utilizing a printer mechanism.
In a conventional printer, a printing head and a ribbon-feed driving section are arranged on a carriage which moves along the longitudinal direction of a platen. A ribbon take-up spindle is engaged with the ribbon-feed driving section so as to feed an ink ribbon or an ink tape inside a ribbon cassette set on the carriage. At the same time, the printing head transfers ink from the ink ribbon or ink tape onto a sheet wound around the platen.
Instead of a conventional reading apparatus for reading a document including characters or figures, an apparatus has been recently proposed to read documents utilizing a printer.
In order to read a document using such a printer, a sheet on which document information is printed is wound around a platen. A ribbon cassette mounted on the carriage is removed, and a line image sensor is mounted instead. Then, as the carriage is moved, the image sensor scans along the widthwise direction of the sheet, and the platen is rotated after reading each line, thereby sequentially reading the document.
However, in a conventional reading apparatus of this type, when the line image sensor is mounted, it is aligned linearly with a thermal head used for printing with respect to the sheet. Therefore, the thermal head itself must be removed. The mounting and removal of the thermal head is a complex procedure, and results in inconvenience. An example of an arrangement wherein the ribbon cassette and the thermal head are removed for reading a document is described in Japanese Patent Disclosure No. 50-3734. Another arrangement is described in Japanese Patent Disclosure No. 59-32833 or Japanese Utility Model Disclosure No. 54-133733. In this arrangement, the thermal head and the image sensor are arranged so as to be offset from a sheet, that is, they are not aligned linearly with respect to the sheet. However, in either arrangement, the thermal head and the image sensor are arranged on a single carriage or unit so that the overall reading apparatus becomes bulky.
In order to read a color image of a document, an image-pickup area-type color image sensor, which uses a dichroic mirror frequently used in a TV camera, may be used. However, since three image sensors for three colors must be used and these image sensors are relatively expensive, the overall apparatus becomes expensive. In another color reading apparatus, a disk surface is divided into three regions in which three filters of three respective colors are arranged. The disk is rotated in front of a general image sensor so that red, blue and green transmission filters alternately oppose the image sensor. When the red transmission filter opposes the image sensor, the image sensor produces a red signal. When the blue transmission filter opposes the image sensor, the image sensor produces a blue signal. When the green filter opposes the image sensor, the image sensor produces a green signal. In such a color reading apparatus, since only a single image sensor need be used, color image reading can be performed at low cost. On the other hand, in a color reading apparatus of the filter type, mounting the respective color filters on a carriage of the printer and a compact arrangement for the replacement of the respective color filters present problems. These problems are considered difficult to solve.